Cathode structure



April 20, 1948. P. KUSCH CATHODE STRUCTURE Filed July 9, 1945 R O T N E V m m H 4 /I\\. a 6 'Z 2 I F m Z 0 F w 62 POLY KARP KUSCH Eitented Apr. 20, 1948 CATHODE STRUCTURE Polykarp Kusch, New York, N. Y., assignor it the United States of Ameri Secretary of War ca as represented by the Application July 9,1945, Serial No. 604,072 Claims. (01. 250-215) and more particularly to such cathodes as are applicable to magnetron tubes.

As magnetrons are used for shorter and shorter wavelengths, the efficiency becomes very low. This low efficiency is in part due to the.bad electrons emitted from the cathode. "Bad electrons are those which are accelerated by the radio frequency field between cathode and anode, and thus absorb energy from this field. Some of these electrons have a path such that they turn around and bombard the cathode with considerable 'ener y, causing what is known as back-heating of the cathode.

Under conditions of very short wavelength, it is necessary, because of the back-heating, to use a comparatively massive cathode for proper cooling. Also, sparking of magnetron cathodes is a common cause of cathode failure, and it has been found that an irregular cathode surface delays such a failure. also desirable to provide a large amount of coating of electron-emitting material on the cathodes in order that suflicient thermionic emission be available after sparking occurs.

Among the objects of this invention, therefore, are:

1. To provide a cathode structure applicable to magnetrons;

2. To provide such a cathode having increased. durability with respect to electron bombardment;

and

3. To provide such a cathode having reduced susceptibility to failure under sparking conditions. 7 V

In accordance with the present invention, there is provided a sleeve-like cathode structure in which the outer surface of the cathode has grooves in both the longitudinal and the circumferential directions. Two heavy supporting tabs are welded to massive cathode supports for eflicient heat conduction.

This invention will best be understood by reference to the drawings, in which:

Fig. 1 illustrates a cross-sectional view and side-view of the blank used for construction of the cathode according to this invention;

Fig. 2 illustrates a cross-sectional view of the central portion of the blank with the circumferential grooves, and a portion of the mandrel used for turning the blank;

Fig. 3 illustrates the same portion of the blank and mandrel of Fig. 2 after a knurling operation;

Fig. 4 illustrates the plan and side view of a tab used for supporting the cathode;

Under sparking conditions it is Fig. 5 is a perspective view of. the cathode and cathode leads in assembled form.

Referring now to the description of the oathode and to one desirable manufacturing process, Fig.0. illustrates a ent-away section of a flanged hollow cylinder which is used as a blank for construction of the cathode, flanges II and I5 acting as two "hats" for preventing the Gadarene effect in magnetrons. In one embodiment of the invention the material used for the oathode was pure nickel.

Circumferential grooves are then cut in the blank by mounting it over a lathe mandrel IS, the details of the grooves I2 being illustrated in the cut-away View ofFig. 2. In an exemplary embodiment of this invention, the grooves were 0.0075 inch wide, with the distance between grooves being 0.0075 inch. With the blank still' in the lathe and on mandrel IS; the cathode surface is then rolled by a fine straightknurl in order to produce longitudinal grooves l8 illustrated in Fig. 5, which are similar to the circumferential grooves l2. Fig. 3 illustrates the dovetail shape of the circumferential grooves 12 after knurling. It is seen that the bottoms [2 of the grooves are wider than the tops M, the dovetail grooves thus acting as anchoring means for an oxide coating 20, Fig. 5, sprayed or painted over the dovetailed and knurled surface of the oathode cylinder l0.

After the-first rotation of the cathode during the knurling operation, it is not important that the knurling tool mesh with previously made indentations for good cathode operation. Knurling in this manner increases slightly the outside dimension of the cathode. In one embodiment, the

outside diameter was increased 0.003 inch from an original value of 0.11 inch.

A supporting tab 20 which could be used in conjunction with the present cathode is illustrated in Fig. 4. These tabs have their circular portions supporting each end of the cathode as illustrated in Fig. 5, and are welded to comparatively massive cathode support leads 22 and 24, which extend through a glass seal 26 to a point outside the tube where cooling fins 28 and 29 may be attached to the cathode rods 22 and 24 for a more eifective dissipation of heat.

With the small compartments 30 that are formed in the cathode structure by virtue of the grooving and knurling operations, it can be seen from Figs. 3 and 5 that unusually large amounts .of coating material 32 may be retained by the cathode. Also, this irregular surface is of such a contour as to bind or to anchor the cathode amoeba with a brush on portion 30 of the cathode. Tabs and 20-A are brazed to the hats l i5, arid to the tungsten rods 22 and. The heater coil, 7

inserted into the hollow pbftiorroi; cylinder, has its upper end 32 brazed to tab 20 and hat II, while its lower end 34 is connected, toajumper 33 an outer conductor 36 of the concentric-line formed by this conductor with tungsten rod 24,

the two being insulated. from each other by an insulatings leeve 39. Conductor 38 is. connected to a rod 40 which eretiuzies' through the, glass seal 26 for completing the ictriial eenneetiens or t heater efeii, As aise' se'a n mace-pen in application 604,073, new Patent o. 2,437,880, filed simultaneously with the filing 'of this, application, the dimensionsof the tungsten rods 22 and 24 are made to'hold the cathodein eerie-eminentionship withrespect tdthe anode when the magnetron reaches, the (seeming, ther'nial, equilibrium. r

The advantages of thedisclosed cathode structure are: Largeamoufitbf the diiid material 32 which is a nchord t6 cy inder It and thus notbe loosened from the, cylinder. because of cyclic heating and cooling of. the cattle-depreduced by the electrons whose curvilinear paths in the interaction ze eet the inaghetren are such as to lead them been to. thecatl'iode during the duty cycles oi; magnetron. The overheating of the cathode is re'tehtea tweaking the ode blankof massiv constfuctiofi setter it'l'ias relatively large calorific inertia,andv 5y dissipating excess of heat through the, relatively thick walls of the c'athod cylinder 10, tabs 2!],- 20-.A, massive tungsten rods 22, 23, and radiators 23 and 23. prio tdthe advent 6f the. aie'elosea cathode the X and -Band maghetreasnad hardly any useful life ecause of short life of cathodes.

While there has been describedv what is at present considered the preferred embodiment of the invention, it will beeptieuetet ese sjli illed in the art that various heiige and ,ir'iodiflcations may be made therein without dpaitingjiom the,

v mman we.i e re eeii i ii fi i' pended claims to cover all such changes and 4 modifications as fall within the true spirit and scope of the invention.

Iclaim:

1. A cathode structure comprising a hollow, flanged metallic cylinder, dovetailed grooves around the outer surface of said cylinder, knurled grooves crossing said dovetailed grooves, and an electronemitting oxide coating anchored to said cylinder by means of said grooves.

2. A cathode structure as defined in claim 1 which also includes two metallic tabs, each havrag-a washer portion and a bar portion, the washer portionof eachtab being brazed to the outer ei repiar 'sufiace-..d the respective flange, and a metallic riod,' coii r iected to each bar portion of I said tab, ibhmechanically supporting said cathod-and for" completing the electrical circuit of said'cathode.

3. A cathode structure comprising a hollow, metallic, machinedcylinder, an integral flange at each end of said cylinder; dovetailed ring-grooves around the outer surface or saidcylindr, straight knurled grooves at right angles-to said ringgrooves, and an electron-emitting oxide layer anchored to said cylinder by said ring g'ro'o'ves and saidknurled grooves.

4. A cathode'structure as defined in claim 3 which fu-rther includes metallic radiators conductiyely connected to said cylinder for cooling said cylinder during the operating cycle of said cathode. I g

5; A cathode structure c'cimprising a hollow, metallic cylinder, an integral flange at each end of said cylinder, dovetailed grooves around the outer surface of said cylinder and additional grooves crossing said. covet-eneagreevee, a metallic hiernlderbrazed to each flange, said metallic member-haying a metallic arm radially extending away from said flange through aglass seal,andradiatingsurfaces atthe outer end of each memb r for c'oolingsaidcylinder during-the operation (if Said cathode. v

P O LYKARP KUSCH.

REFERENCES*CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name 4 Date 7 1,866,195 Creuz'e July 5, 1932 1,891,074 Winter Dec. 13, 1932 1,946,603 Von Wedel Feb. 13, 1934 2,095,337 Lop'pa'cker Oct. 12, 1937 2,103,362 Hansell Dec-28, 1937 

